Method of programming a semiconductor memory

ABSTRACT

A method of programming a semiconductor memory includes forming a multiplicity of fuse links in at least two mutually parallel planes in a semiconductor body, and separating the fuse links from one another with an electrical insulator. It also includes irradiating a selected fuse link with at least two laser beams and melting the selected fuse link by crossing the laser beams at the selected fuse link.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 09/143,122,filed Aug. 28, 1998, now U.S. Pat. No. 6,180,992.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention belongs into the semiconductor technology field. Morespecifically, the invention pertains to a method of programming asemiconductor memory, having a multiplicity of fuses which are providedon a semiconductor body and can each be programmed individually throughthe injection of energy to break or make a conducting connection.

It is well-known to use fuses for the permanent storage of data insemiconductor storage devices and for programming the redundancy insemiconductor storage devices of this type. In the former case, thestate of the fuse (“conducting” or “nonconducting”) establishes a datavalue (“0” or “1”), while in the latter case, if there is a defectivestorage cell, a redundant storage cell is connected into the circuit byactivating the fuse.

Fuses generally consist of, for example, polycrystalline silicon or asimilar suitable material that can be fused or melted through the actionof energy, by means of which a previously existing conducting connectionis broken. It is, however, also conceivable to use a material which isconverted by the action of energy from the nonconducting state to theconducting state, in order thus to create a conducting connection. Itwill nevertheless be assumed below that a previously existing conductingconnection will be destroyed by the action of energy.

The action of energy may be brought about, for example, by irradiating afuse with a laser beam, or else simply by passing a relatively heavycurrent through a particular fuse, in order to cause it to melt.

Contemporary fuse configurations use fuses which are arranged next toone another, for example in the form of a matrix, on the surface of thesemiconductor body, or chip, of a semiconductor storage device. As thenumber of fuses rises, that is to say as the storage capacity of thesemiconductor storage device increases, the overall effect is that therequired area of the chip becomes ever greater.

In order to keep the required area as small as possible, attempts haveto date been made to design the fuses as small as possible in geometricterms. However, that procedure is limited by the fact that, when thefuse is activated or programmed, i.e. for example when the fuses areilluminated with a laser beam, a minimum mutual separation of theindividual fuses must be respected so that the desired fuse candeliberately and reliably be melted by the laser beam.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method ofprogramming a semiconductor memory, which overcomes the above-mentioneddisadvantages of the prior art devices and methods of this general typeand which is distinguished by a considerably reduced area requirement,yet in which individual fuses can be activated deliberately andreliably.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a method of programming a semiconductormemory, comprising a semiconductor body and a multiplicity of fusesdisposed in the semiconductor body, the fuses being arranged in at leasttwo planes and being programmable by a superposition of at least twolaser beams crossing at a respective fuse to be programmed.

In other words, the objects of the invention are satisfied with afusible link configuration disposed in at least two planes on thesemiconductor body. The fuses may be arranged above one another inseveral, say, n planes. The area required by the fuses on thesemiconductor body is therefore reduced approximately by a factor n, ifthe wiring for connecting the fuses is disregarded.

In accordance with an added feature of the invention, an insulatinglayer is disposed between the planes of the fuses. The insulator ispreferably silicon dioxide.

In accordance with another feature of the invention, the fuses consistof polycrystalline silicon. The polycrystalline silicon links can bemelted by passing a current through them or by superimposed action of atleast two laser beams, in order thus to activate (or deactivate) thefuses. The two acting laser beams then cross at the fuse to beactivated.

Accordingly, there is also provided, in accordance with the invention, amethod of programming a semiconductor memory, which comprises:

forming a multiplicity of fuse links in at least two mutually parallelplanes in a semiconductor body, and separating the fuse links from oneanother with an electrical insulator; irradiating a selected fuse linkwith at least two laser beams and melting the selected fuse link bycrossing the laser beams at the selected fuse link.

Where several fuse planes are arranged above one another, the fuses canbe programmed either by a specific current, which causes the material tomelt, or alternatively by the superimposition of several laser beams.The intensity of the laser beams should be chosen such that just asingle beam will not damage the material; however, if a plurality ofbeams are superimposed at one point (the location of the fuse to beprogrammed), then the local energy intensity will become great enoughfor the fuse to be destroyed.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method of programming a semiconductor memory, it is neverthelessnot intended to be limited to the details shown, since variousmodifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawing figure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fuse configuration in two planes, witha separating insulator layer having been omitted for purposes ofclarity; and

FIG. 2 is a partial sectional view through a semiconductor body and thefuse configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures of the drawing in detail, there is seen aplurality of polycrystalline silicon fuses 1. The fuses are arranged intwo planes 2, 3 above one another in the z direction on a surface of asemiconductor body 10. The fuses extend in the x-y plane, of thesemiconductor body 10 and they are separated from one another by asilicon dioxide insulator layer.

A fuse 4 to be programmed is exposed to two laser beams 5, 6 which crossat a point 7 in the region of the fuse 4. The fuse 4 is thereby meltedand thus broken. The energy of the laser beams 5, 6 is adjusted suchthat one beam alone cannot cause any melting, and this ensures that onlythe fuse 4 where the laser beams 5, 6 cross is deliberately destroyed,while the other fuses 1 remain undamaged.

As an alternative to the intersecting laser beams 5, 6, it is alsopossible to pass a current through the fuse 4, such that this fuse 4 ismelted and therefore destroyed.

We claim:
 1. A method of programming a semiconductor memory, whichcomprises: forming a multiplicity of fuse links in at least two mutuallyparallel planes in a semiconductor body, and separating the fuse linksfrom one another with an electrical insulator; irradiating a selectedfuse link with at least two laser beams and melting the selected fuselink by crossing the laser beams at the selected fuse link.